JP2002319390A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance a charge-discharge characteristic, a load factor characteristic and an output characteristic, in a nonaqueous electrolyte secondary battery using a carbon material capable of storing and releasing lithium ion as a negative electrode. SOLUTION: The the negative electrode containing the first carbon material capable of storing and releasing lithium ion, and the second carbon material having 10 m<2> /g or more of specific surface area, and a positive electrode containing lithium-manganese compound capable of storing and releasing lithium ion are used in this nonaqueous electrolyte secondary battery.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-aqueous electrolyte secondary battery using a carbon material capable of occluding and releasing lithium ions as a negative electrode.

[0002]

2. Description of the Related Art In recent years, the size and weight of portable electronic devices has been remarkably reduced, and accordingly, there has been a great demand for a battery as a power supply to be reduced in size and weight. To meet such demands, various secondary batteries have been developed.Currently, lithium ion batteries using lithium cobalt oxide, which is a composite oxide having a layered structure as a positive electrode active material, have a high operating voltage, Since it has a high energy density, it is suitable for the above applications. However, lithium cobaltate is scarce in resources,
Due to the high cost, lithium manganese compounds have been proposed as substitutes.

[0003] As a negative electrode active material of this type of battery, a carbon material capable of occluding and releasing lithium ions is currently used.

[0004]

However, when a lithium-containing manganese composite oxide as a positive electrode active material is exposed to an electrolytic solution for a long time or at a high temperature, manganese (Mn) is converted from the positive electrode into the electrolytic solution. Since the elution amount increases, manganese adheres to the carbon material of the negative electrode. This causes an increase in the charge transfer resistance of the negative electrode and a problem that the charge / discharge cycle characteristics, load factor characteristics, and output characteristics of the battery are deteriorated because the lithium ion occlusion / release sites in the carbon material are blocked. .

In view of the above situation, the present invention provides a negative electrode having improved charge / discharge cycle characteristics, load factor characteristics, and output characteristics, and uses the above-described negative electrode to provide a non-aqueous liquid excellent in charge / discharge performance. An object is to provide an electrolyte secondary battery.

[0006]

According to a first aspect of the present invention, there is provided a non-aqueous electrolyte secondary battery comprising: a first carbon material capable of occluding and releasing lithium ions; and a second carbon material having a specific surface area of 10 m ² / g or more. And a positive electrode containing a lithium manganese compound capable of inserting and extracting lithium ions.

According to the first aspect of the present invention, since the negative electrode contains the second carbon material, manganese is captured by the second carbon material in the negative electrode, and the adhesion of manganese to the first carbon material is suppressed. Thereby, the increase in the charge transfer resistance of the first carbon material is suppressed, and the occlusion / release of lithium ions in the first carbon material is suppressed, and the charge / discharge cycle characteristics of the battery are reduced. A non-aqueous electrolyte secondary battery having excellent load factor characteristics and output characteristics can be obtained.

According to a second aspect of the present invention, in the nonaqueous electrolyte secondary battery, the second carbon material is carbon black.

According to the second aspect of the invention, the current collection performance of the negative electrode is improved, and the manganese trapping performance is further improved.

According to a third aspect of the present invention, in the nonaqueous electrolyte secondary battery, the second carbon material is contained in an amount of 0.1 to 10% by weight based on the first carbon material.

According to the third aspect of the present invention, the amount of the second carbon material contained in the negative electrode is reduced as much as possible.
The capacity of the negative electrode can be increased by increasing the amount of the first carbon material as an active material included in the negative electrode.

According to a fourth aspect of the present invention, in the non-aqueous electrolyte secondary battery, the lithium manganese compound has a composition formula of Li _x M
_{n 2-y M y O 4} (0 ≦ x ≦ 1.4; 0 ≦ y ≦ 1.8;
M is characterized by being represented by one or more transition metal elements).

According to the invention of claim 4, manganese is captured by the second carbon material in the negative electrode, and a nonaqueous electrolyte secondary battery having excellent charge / discharge cycle characteristics, load factor characteristics and output characteristics can be obtained. .

According to a fifth aspect of the present invention, in the non-aqueous electrolyte secondary battery, the lithium manganese compound has a composition formula of Li _x M
n _{1-y MyO 2} (0 ≦ x ≦ 1.4; 0 ≦ y ≦ 0.9;
M is characterized by being represented by one or more transition metal elements).

According to the invention of claim 4 or claim 5,
Manganese is captured by the second carbon material in the negative electrode, and a nonaqueous electrolyte secondary battery having excellent charge / discharge cycle characteristics, load factor characteristics, and output characteristics can be obtained.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows the appearance of a nonaqueous electrolyte secondary battery provided with a long cylindrical power generating element of the present invention, and FIG. 2 shows the appearance of the power generating element. In FIG. 1, 1 is a non-aqueous electrolyte secondary battery, 2 is a battery case, 3 is a battery cover, 4 is a positive electrode terminal,
Reference numeral 5 denotes a negative electrode terminal, 6 denotes a safety valve, and 7 denotes an electrolyte injection port.
In FIG. 2, reference numeral 8 denotes a power generating element, 9 denotes a positive electrode, 10 denotes a negative electrode, and 11 denotes a separator.

As shown in FIGS. 1 and 2, the nonaqueous electrolyte secondary battery of the present invention has a power generating element 8 in which a positive electrode 9 and a negative electrode 10 are wound in an oval shape with a separator 11 interposed therebetween.
Is stored in the battery case 2, the battery case 2 and the battery cover 3 are welded, and then a non-aqueous electrolyte is injected from the electrolyte injection port 7. The positive electrode, the separator, the electrolyte, and the like used in the nonaqueous electrolyte secondary battery are not particularly different from those conventionally used, and commonly used ones can be used.

The present invention relates to a non-aqueous electrolyte secondary battery,
A first carbon material capable of inserting and extracting lithium ions;
It is characterized by using a negative electrode containing a second carbon material having a specific surface area of 10 m ² / g or more and a positive electrode containing a lithium manganese compound.

In a non-aqueous electrolyte secondary battery using a positive electrode containing a lithium manganese compound as an active material, when the lithium manganese compound is exposed to the electrolyte for a long time, manganese (L) is converted from the lithium manganese compound into the electrolyte. Mn)
Is eluted. Then, the manganese eluted in the electrolytic solution reaches the negative electrode, manganese adheres to the first carbon material as the negative electrode active material, the charge transfer resistance of the first carbon material increases, and further, the manganese becomes the first carbon material. The charge / discharge performance of the battery is reduced because the carbon material occludes sites for absorbing and releasing lithium ions. The lithium manganese compound may be used alone or in combination of two or more.

Therefore, the present invention, as a countermeasure against this, includes a second carbon material having a specific surface area of 10 m ² / g or more in the negative electrode, and the second carbon material having a large surface area selectively removes manganese coming to the negative electrode. By trapping, the increase in the charge transfer resistance of the negative electrode is suppressed, and the deterioration of the negative electrode is prevented by securing sites for absorbing and releasing lithium ions in the carbon material. As a result, the charge-discharge cycle characteristics, An object of the present invention is to obtain a nonaqueous electrolyte secondary battery having excellent load factor characteristics and output characteristics.

In the present invention, as the second carbon material, a carbon black having a specific surface area of 10 m ² / g or more, such as acetylene black, ketchen black or furnace black, may be used alone or in combination of two or more. By doing so, the current collecting performance of the negative electrode is improved, and the current collecting performance of the negative electrode is further improved, and the manganese capturing performance is further improved. The specific surface area of the second carbon material is 10
If it is less than m ² / g, the function of selectively capturing manganese coming to the negative electrode is poor, and the first carbon material is greatly deteriorated.

Further, the amount of the second carbon material contained in the negative electrode is set to be 0.1 to 10% by weight based on the first carbon material, so that the amount of the second carbon material contained in the negative electrode is reduced as much as possible. As a result, the capacity of the negative electrode can be increased by increasing the amount of the first carbon material contained in the negative electrode. When the amount of the second carbon material relative to the first carbon material is 0.1 wt% or less, a negative electrode having a small charge transfer resistance cannot be obtained. When the amount is 10 wt% or more, the ratio of the negative electrode active material decreases. Becomes smaller. In addition,
The amount of the second carbon material with respect to the first carbon material is preferably in the range of 0.1 to 1 wt%, since increasing the first carbon material as much as possible increases the capacity of the battery.

As the positive electrode active material, various lithium manganese compounds capable of inserting and extracting lithium ions can be used. Among them, the composition formula Li _x Mn _{2 -y My 0 4}
(0 ≦ x ≦ 1.4; 0 ≦ y ≦ 1.8; M is a transition metal element composed of one or more kinds) or a composition formula Li _x Mn _{1- y My} O ₂ (0 ≦ x ≦ 1.4; 0 ≦ y ≦
0.9; M is a transition metal element composed of at least one kind), which is more useful for improving battery performance.

In the present invention, the type of the first carbon material is not particularly limited, and a mixture of one or more types of non-graphitizable carbon, graphitizable carbon, natural graphite or artificial graphite can be used. is there.

Examples of the binder used for the electrode include polyvinylidene fluoride which is widely used, polytetrafluoroethylene as another binder, styrene-butadiene rubber as a rubber-based polymer, and cellulose-based and rubber-based polymers. Examples thereof include a mixture with a polymer or a copolymer mainly containing polyvinylidene fluoride.

The organic solvent of the electrolytic solution used in the non-aqueous electrolyte secondary battery of the present invention is not particularly limited. For example, ethers, ketones, lactones, nitriles, amines, amides, sulfur compounds, halogen compounds Hydrocarbons, esters, carbonates, nitro compounds, phosphate ester compounds, sulfolane hydrocarbons, etc., among which ethers, ketones, esters, lactones, halogens Hydrocarbons, carbonates and sulfolane compounds are preferred. Examples of these include tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, anisole, monoglyme, 4-methyl-2-pentanone, ethyl acetate, methyl acetate, methyl propionate, ethyl propionate,
2-dichloroethane, γ-butyrolactone, dimethoxyethane, methylformate, dimethyl carbonate,
Methyl ethyl carbonate, diethyl carbonate, propylene carbonate, ethylene carbonate, vinylene carbonate, dimethylformamide, dimethyl sulfoxide, dimethylthioformamide, sulfolane,
Examples include -methyl-sulfolane, trimethyl phosphate, triethyl phosphate, and a mixed solvent thereof, but are not necessarily limited thereto. Preferred are cyclic carbonates and cyclic esters. Most preferably, it is an organic solvent of a mixture of one or more of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, and diethyl carbonate.

The electrolyte salt used in the non-aqueous electrolyte secondary battery of the present invention is not particularly limited, but may be LiClO ₄ ,
LiBF ₄ , LiAsF ₆ , CF ₃ SO ₃ Li, LiP
F ₆ , LiPF ₃ (C ₂ F ₅ ) ₃ , LiN (CF ₃ SO
₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiI, LiA
1Cl _{4 and the} like and mixtures thereof. Preferably, a lithium salt in which one or more of LiBF ₄ and LiPF ₆ are mixed is preferable.

In addition, a solid ion-conductive polymer electrolyte can be used as an auxiliary for the above-mentioned electrolyte. In this case, as a configuration of the non-aqueous electrolyte secondary battery, a combination of a positive electrode, a negative electrode and a separator with an organic or inorganic solid electrolyte and the above non-aqueous electrolyte, or a positive electrode, an organic or inorganic solid electrolyte as a negative electrode and a separator A combination of the membrane and the above-mentioned non-aqueous electrolyte may be used. When the polymer electrolyte membrane is made of polyethylene oxide, polyacrylonitrile, polyethylene glycol, or a modified product thereof, the polymer electrolyte membrane is lightweight and flexible, which is advantageous when used for a wound electrode plate. Further, in addition to the polymer electrolyte, an inorganic solid electrolyte or a mixed material of an organic polymer electrolyte and an inorganic solid electrolyte can be used.

The shape of the power generating element of the non-aqueous electrolyte secondary battery of the present invention may be any of various shapes such as a wound type, a folding type, and a stack type. As the shape of the battery, batteries having any shape such as a square shape, a cylindrical shape, and a long cylindrical shape can be used.

[0030]

EXAMPLES Examples of the present invention will be described below together with comparative examples.

Example 1 Specific surface as first carbon material
The product is 2.7m²/ G of massive graphite as the second carbon material
Has a specific surface area of 28m²/ G acetylene black
Thus, a negative electrode was prepared. 87.12 wt% of massive graphite
0.88 wt% of acetylene black,
Mixing vinylidene fluoride (PVdF) 12wt%
N-methyl-2-pyrrolidone (NM
P) was added to adjust the viscosity. This viscous body has a thickness of 1
6μm copper foil, vacuum dried at 150 ℃, solvent
Is completely volatilized, and the applied weight of the negative electrode mixture is reduced.
1.646g ・ 100cm^-2I tried to be. Soshi
And the electrode area is 3cm²Now the electrode porosity will be 30%
After roll pressing, this is used as a negative electrode,
Using lithium metal for the reference electrode and 1 mol · dm for the electrolyte
^-3LiClO₄And 5 × 10^-4mol · dm ^-3of
Mn (ClO₄)₂Was dissolved in 0.03
dm³Thus, the battery A of Example 1 was manufactured.

COMPARATIVE EXAMPLE 1 A mass of negative electrode mixture of a mass of graphite
Battery B of Comparative Example 1 was produced in the same manner as in Example 1, except that t% and polyvinylidene fluoride (PVdF) were 12 wt%.

Comparative Example 2 A battery C of Comparative Example 2 was produced in the same manner as in Example 1 except that acetylene black having a specific surface area of 9 m ² / g was used as the second carbon material.

The discharge capacities of the batteries A and B were measured. Both batteries were charged with a current of 0.5 mA · cm ^{−2 to} a potential of 0.0 V (vs. lithium metal),
The discharge capacity at the time of discharging at a current of 0.5 mA · cm ^{−2 to} a potential of 1.5 V (vs. lithium metal) was measured.

Then, charging and discharging are repeated under these conditions.
The discharge capacity per 1 g of the negative electrode active material containing acetylene black after charging and discharging for 0 cycles was calculated, and the discharge capacity was calculated by dividing the discharge capacity by the initial discharge capacity. Also,
To evaluate the load factor characteristics after the cycle, 0.5 mA
After charging to a potential of 0.0 V (with respect to lithium metal) with a current of cm ⁻² , 1.25 mA · cm ⁻² and 2.5 mA ·
The discharge capacity was measured when the battery was discharged to a potential of 1.5 V (with respect to lithium metal) at currents of cm ⁻² and 5 mA · cm ⁻² . Table 1 shows the evaluation results.

[0036]

[Table 1]

Battery A of Example 1 and Battery B of Comparative Example 1
FIG. 3 plots the relationship between the discharge current and the discharge capacity after 50 cycles. In FIG. 3, the symbol ● represents the battery A of Example 1, the symbol ○ represents the battery B of Comparative Example 1, and the symbol Δ represents
Indicates the characteristics of the battery C of Comparative Example 2.

As can be seen from Table 1 and FIG. 3, in the battery A of Example 1 using the negative electrode containing acetylene black having a specific surface area of 28 m ² / g according to the present invention, since the charge transfer resistance was small, the discharge capacity retention rate was low. High, even if the discharge current is increased,
The large discharge capacity showed excellent load factor characteristics. On the other hand, in the battery B of the comparative example 1 containing no acetylene black and the battery C of the comparative example 2 using the negative electrode containing acetylene black having a specific surface area of 9 m ² / g, the function of selectively capturing manganese in each case was used. The battery A of Example 1 was inferior in characteristics due to poor battery performance.

Example 2 This battery is a long cylindrical non-aqueous electrolyte secondary battery having a designed capacity of 11.6 Ah as shown in FIG. The positive electrode is LiNi _0.55 Co _0.15 Mn
_0.30 O ₂ , polyvinylidene fluoride (PVdF), and acetylene black were mixed, NMP was added thereto to form a paste, and the mixture was applied on an aluminum foil and dried to form a positive electrode mixture layer. . The same negative electrode as that used in Example 1 was used. The strip-shaped negative electrode and the positive electrode manufactured in this manner were, as shown in FIG.
After forming an electrode group by winding it into an oval shape via a separator, inserting this electrode group into an elongated cylindrical bottomed aluminum container, and further filling the core of the electrode group with a filler, The electrolyte was injected, the container and the lid were welded by laser welding, and the battery D of Example 2 was produced.

Comparative Example 3 A battery E of Comparative Example 3 was prepared in the same manner as in Example 2, except that the same negative electrode as that used in Comparative Example 1 was used.

10. Design capacity manufactured as described above.
Using a large battery of 6 Ah, 8 V to 4.1 V at 2 A current
Time, charge with constant current / constant voltage, 2.7A with 2A current
The discharge capacity when discharging to a voltage of V was measured. Also,
The output density at each depth of discharge (DOD) with respect to the discharge capacity was calculated according to SAE standard J1798 draft. Table 2 shows the evaluation results.

[0042]

[Table 2]

Battery D of Example 2 and Battery E of Comparative Example 3
FIG. 4 plots the relationship between DOD and power density. In FIG. 4, the symbol ● indicates the characteristics of the battery D of Example 2, and the symbol ○ indicates the characteristics of the battery E of Comparative Example 3.

From Table 2 and FIG. 4, the battery D of Example 2 exhibited a higher power density for each DOD than the battery E of Comparative Example 3. It is considered that such a test result is due to a decrease in the charge transfer resistance of the negative electrode active material.

[0045]

As is apparent from the above, the negative electrode of the present invention is useful for improving a negative electrode for the purpose of improving charge / discharge cycle characteristics, load factor characteristics and output characteristics.
Furthermore, by using an inexpensive lithium manganese compound for the positive electrode, it can be said that its use value is extremely high as compared with the lithium cobalt composite oxide that is currently widely used.

[Brief description of the drawings]

FIG. 1 is a diagram showing the appearance of a long cylindrical nonaqueous electrolyte secondary battery.

FIG. 2 is a view showing the appearance of a long cylindrical power generating element.

FIG. 3 is a diagram showing a relationship between discharge current and discharge capacity of a battery A of Example 1, a battery B of Comparative Example 1, and a battery C of Comparative Example 2. .

FIG. 4 shows a battery D of Example 2 and a battery E of Comparative Example 3,
The figure which shows the relationship between DOD and an output density.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Non-aqueous electrolyte secondary battery 2 Battery case 3 Battery cover 4 Positive electrode terminal 5 Negative terminal 6 Safety valve 7 Electrolyte inlet 8 Long cylindrical power generation element 9 Positive electrode 10 Negative electrode 11 Separator

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5H029 AJ02 AJ05 AK03 AL06 AL07 AM02 AM03 AM04 AM05 AM07 AM12 AM16 BJ02 DJ08 EJ04 HJ01 HJ02 HJ07 5H050 AA02 AA07 BA17 CA09 CB07 CB08 CB29 DA10 EA10 HA01 HA02 HA07

Claims (5)

[Claims] 1. A first type capable of inserting and extracting lithium ions.
A non-aqueous material characterized by using a negative electrode containing a carbon material of the formula (1) and a ^second carbon material having a specific surface area of 10 m ² / g or more, and a positive electrode containing a lithium manganese compound capable of inserting and extracting lithium ions. Electrolyte secondary battery. 2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the second carbon material is carbon black. 3. The non-aqueous electrolyte secondary battery according to claim 1, wherein the negative electrode contains 0.1 to 10 wt% of the second carbon material with respect to the first carbon material. 4. A lithium manganese compound having the composition formula Li _x
Mn _{2-y MyO 4} (0 ≦ x ≦ 1.4; 0 ≦ y ≦ 1.
8. The non-aqueous electrolyte secondary battery according to claim 1, 2 or 3, wherein M is represented by at least one transition metal element. 5. The lithium manganese compound having the composition formula Li _x
Mn _{1-y MyO 2} (0 ≦ x ≦ 1.4; 0 ≦ y ≦ 0.
9. The nonaqueous electrolyte secondary battery according to claim 1, wherein M is represented by at least one transition metal element.